The present invention relates generally to digital cellular mobile or cordless telephone systems, and more specifically to a handoff technique for switching communication paths of cordless stations when crossing a cell boundary without interruptions.
A prior art cellular switching system for mobile stations includes a time-division switch to which line interface circuits are terminated. In addition to subscriber stations, base stations are coupled by land lines to the line interface circuits to establish radio links to mobile stations such as cordless telephones or portable data terminals. The base stations are located in respective cells to serve home mobile stations, which may roam across from one cell to another. To ensure uninterrupted channel switching between base stations of adjacent cells when a mobile station is crossing their boundaries, several three-way conference circuits are terminated to the time-division switch through associated line interface circuits. One of the three-way conference circuits is switched to the base stations, as well as to a destination station to which the mobile station is connected. The mobile station transmits its signal to both base stations through separate paths. In the conference circuit, different versions of the transmitted signal are received and combined together to produce an average value, which is then combined with a signal from the destination station. This arrangement allows the mobile station to switch its channel to the new cell site without interruption.
However, if the information being transmitted is a data signal, it is impossible for the three-way conference circuit to ensure transparency for data signals.